Modern vehicles are becoming increasingly reliant on electrical systems and, consequently, electrical power. Likewise, conventional electrical systems for vehicles have become more sophisticated and, in some cases, are linked together with the numerous other electrical systems by their respective electrical control units, or “ECUs.” Such electrical systems range from a conventional AM/FM radio, engine management system, and/or an antilock braking system (ABS), to modern infotainment systems, instrument panels, and security systems. Many of these electrical systems power-down when the vehicle is turned off, and power-up when the vehicle is turned on. At least some of the electrical systems in modern vehicles operate continuously, even when the vehicle is turned off, including, for example, security systems, instrument panels, infotainment systems, and keyless entry, or “fob,” systems.
Many vehicles that incorporate electrical systems that are powered continuously utilize the vehicle's onboard electrical power source, e.g., a battery. Such electrical systems generally operate in an “idle” or “sleep” mode that reduces their power demands as compared to when the vehicle is running and drawing power from, for example, an alternator or other electrical power conversion system. Accordingly, the vehicle's “quiescent” electrical load, i.e., the electrical load when the vehicle is turned off, is typically small enough, e.g., 5 milliamps to 200 milliamps, that the vehicle's battery is not so depleted that the vehicle becomes disabled. A need exists, however, to supplement an vehicle's onboard power source to supply electrical power for the vehicle's quiescent electrical load, which has tended to increase over the many years of development in the vehicle industry.